函数与控制流

fn add(a: i32, b: i32) -> i32 {
    a + b          // 无分号 = 返回值（表达式）
}
 
fn main() {
    let r = add(2, 3);
    println!("{}", r);
}

fn main() {
    let n = 7;
    let desc = if n % 2 == 0 { "偶数" } else { "奇数" };
    println!("{} 是 {}", n, desc);
}

fn main() {
    // loop：无限循环，用 break 退出并可带值
    let mut i = 0;
    let result = loop {
        i += 1;
        if i == 5 { break i * 10; }
    };
    println!("loop 结果 = {}", result);
 
    // while：条件循环
    let mut n = 3;
    while n > 0 {
        n -= 1;
    }
 
    // for：遍历集合，最常用
    for x in 0..3 {
        println!("x = {}", x);
    }
}

fn describe(n: i32) -> &'static str {
    match n {
        0 => "零",
        1 | 2 => "小",
        3..=9 => "个位数",
        _ => "其他",     // 通配，保证穷尽
    }
}
 
fn main() {
    println!("{}", describe(0));
    println!("{}", describe(2));
    println!("{}", describe(5));
    println!("{}", describe(100));
}

fn main() {
    'outer: for i in 0..3 {
        for j in 0..3 {
            if i + j == 2 { break 'outer; }
        }
    }
}